The present invention relates to systems and methods for obtaining optimized EPO dosage regimens for a desired pharmacodynamic/pharmacokinetic response.
Erythropoietin (EPO) is the principal factor responsible for the regulation of red blood cell production during steady-state conditions and for accelerating recovery of red blood cell mass following hemorrhage. EPO is a glycoprotein hormone with a molecular mass of 30 KDa and is heavily glycosylated, which serves to protect the EPO molecule from rapid degradation in vivo. Serum EPO concentrations in humans normally range from 6 to 32 U/l (l), and the half-life (t1/2) of EPO is reported to range from 2 to 13 hours with a volume of distribution close to plasma volume. As expected for a large sialoglycoprotein, less than 10% of EPO is excreted in the urine (see, e.g., Lappin et al., 1996. Clin. Lab Haem. 18:137-145.)
The primary site for EPO synthesis in adult organisms is the kidney; although the liver and bone marrow have also been implicated, the data remains inconclusive. The primary stimulus for increased EPO synthesis is tissue hypoxia, which results from decreased oxygen availability in the tissues. Hypoxia can result from the loss of large amounts of blood, destruction of red blood cells by radiation, or exposure to high altitudes. In addition, various forms of anemia cause hypoxia since red blood cells are responsible for oxygen transport in the body. In the normal state, an increased level of EPO stimulates the production of new red blood cells thereby raising the level of oxygen and reducing or eliminating the hypoxic condition.
The principal function of EPO is to act synergistically with other growth factors to stimulate the proliferation and differentiation of erythrocytic progenitor cells in the bone marrow leading to reticulocytosis and increased RBC numbers in the blood, a process also known as erythropoiesis (FIG. 1). During erythropoiesis, cell differentiation along the erythroid lineage occurs over a two week span in humans. The earliest progenitor is the BFU-E (Burst-Forming Unit-Erythroid), which is small and without distinguishing histologic characteristics. The stage after the BFU-E is the CFU-E (Colony Forming Unit-Erythroid), which is larger than the BFU-E and immediately precedes the stage where hemoglobin production begins. The cells that begin producing hemoglobin are the immature erythrocytes, which not only begin producing hemoglobin, but also start condensing their nuclei to eventually become mature erythroblasts. The mature erythroblasts are smaller than the immature erythrocytes and have a tightly compacted nucleus, which is expelled as the cells become reticulocytes. Reticulocytes are so named because these cells contain reticular networks of polyribosomes and as the reticulocytes lose their polyribosomes, they become mature red blood cells (RBCs).
Until recently, the availability of EPO has been very limited. Although the protein is present in human urine, excreted levels are too low to make this a practical source of EPO for therapeutic uses. The identification, cloning, expression of genes encoding EPO and EPO purification techniques, e.g., as described in U.S. Pat. Nos. 4,703,008, 5,389,541, 5,441,868, 5,614,184, 5,688,679, 5,888,774, 5,888,772, and 5,856,298, has made EPO readily available for therapeutic applications. A description of the purification of recombinant EPO (rHuEPO) from cell medium that supported the growth of mammalian cells containing recombinant EPO plasmids for example, is included in U.S. Pat. No. 4,667,016. This recombinant EPO has an amino acid sequence identical to that of human urinary erythropoietin, and the two are indistinguishable in chemical, physical and immunological tests. The expression and recovery of biologically active recombinant EPO from mammalian cell hosts containing the EPO gene on recombinant plasmids has made available quantities of EPO suitable for therapeutic applications. In addition, knowledge of the gene sequence and the availability of larger quantities of purified protein has led to a better understanding of the mode of action of this protein.
The biological activity of a protein is dependent upon its structure. In particular, the primary structure of a protein, i.e., its amino acid sequence, provides information that allows the formation of secondary (e.g., xcex1-helix or xcex2-pleated sheet) and tertiary (overall 3-dimensional folding) structures by a polypeptide during and after synthesis. Furthermore, not only is the biological activity of a protein governed by its structure, but also by modifications generated after the protein has been translated. Indeed, many cell surface proteins and secretory proteins are modified by one or more oligosacchride groups. This modification known as glycosylation, can dramatically affect the physical properties of proteins and can be important in protein stability, secretion, and subcellular localization. Proper glycosylation can be essential for biological activity.
Both human urinary derived and recombinant EPO (expressed in mammalian cells) having the amino acid sequence 1-165 of human EPO contain three N-linked and one O-linked oligosacchride chains which together comprise about 40% of the total molecular weight of the glycoprotein. The oligosacchride chains have been shown to be modified with terminal sialic acid residues. Enzymatic treatment of glycosylated EPO to remove all sialic acid residues results in a loss of in vivo activity, but does not affect its in vitro activity (Lowy et al., 1960, Nature 185:102; Goldwasser et al., 1974, J. Biol. Chem. 249:4202). This behavior has been explained by rapid clearance of asialoerythropoeitin from the circulation upon interaction with the hepatic asialoglycoprotein binding protein (Morrell et al., 1968, J. Biol. Chem. 243:155; Briggs et al., 1974, Am. J. Physiol. 227:1385; and Ashwell et al., 1978 Methods of Enzymol. 50:287). Thus, EPO possesses in vivo biological activity only when it is sialylated to avoid binding by the hepatic binding protein.
Deficient (or inefficient) EPO production relative to hemoglobin level is associated with certain forms of anemia. These include anemia of renal failure and end-stage renal disease, anemia of chronic disorders (chronic infections and rheumatoid arthritis), autoimmune disease, acquired immune deficiency disease (AIDS), and malignancy. Many of these conditions are associated with the generation of a factor that has been shown to be an inhibitor of EPO activity. Other anemias are clearly EPO-independent, and include aplastic anemia, iron deficiency anemia, the thalassemias, megaloblastic anemia, pure red cell aplasia, and myelodysplastic syndromes.
The measurement of EPO levels in human serum has clinical importance. Determination of EPO levels in patient serum can be useful in distinguishing those anemias and polycythemias that are associated with decreased or increased EPO levels from those that are not. Additionally, the demonstration of an inappropriately low level of serum EPO is a prerequisite for concluding that an anemic patient may benefit from treatment with exogenous EPO.
In clinical trials, Epoetin alfa has been evaluated in normal patients as well as in patients with various anemic conditions. Epoetin alfa induces a brisk haematological response in normal human volunteers, provided that adequate supplies of iron are available to support increased hemoglobin synthesis. A majority of trials have investigated the safety and effectiveness in the treatment of anemia associated with renal failure. In addition, Epoetin alfa may be used to correct anemia in other patient groups including anemia associated with platinum-based cancer chemotherapy, anemia associated with zidovudine therapy in patients with AIDS, and anemia associated with other drugs such as cisplatin. Also, the administration of Epoetin alfa has many other potential therapeutic applications: Epoetin alfa administration increases the capacity for autologous blood donation in patients scheduled to undergo surgery and attenuates the decrease in hemocrit often seen in untreated autologous donors; Epoetin alfa administration increases red blood cell recovery after allogeneicxe2x80x94but not autologousxe2x80x94bone marrow transplant; and administration of Epoetin alfa has been shown to improve the quality of life in individuals afflicted with rheumatoid arthritis
An alternative application of EPO is for enhancing the performance of athletes by causing an increase in the hematocrit of the athlete. This augmentation in hematocrit increases the capacity of oxygen transported from the lungs to the exercising skeletal muscles. Since the synthesis of EPO by bioengineering, injecting athletes with EPO, also known as blood doping, has become popular in sports in general, and in particular, cycling (Scheen, A J., 1998. Rev. Med. Liege 53(8): 499-502).
Presently, there are a number of disadvantages associated as the standard EPO dosage regimen administered to patients. In specific indications, such as cancer, subjects are treated with 150 IU/kg of EPO three times per week. Thus, it remains an important goal to change the currently approved dosing schedule to a more convenient dosing schedule and regimen. It is expected that a less frequent administration will improve user acceptance and convenience. Moreover, the standard dosing regimens may not maximize the patient""s physiological response; and standard dosing regimens may not be the most cost efficient.
Furthermore, there are a number of disadvantages associated with the route of EPO administration: regular intravenous administration is inconvenient for the patient; intravenous administration is impractical for individuals afflicted with certain conditions such as continuous ambulatory peritoneal dialysis and non-dialysis patients with restricted vascular access; the rapid dose delivery of rHuEPO via intravenous administration results in a lower bioavailability of rHuEPO for longer time periods and may not be as effective for stimulating production of RBC as desired.
Hence, for all of the reasons detailed above, a better route of administration and means for determining an effective dose and dosage regimen for EPO administration is needed.
Therefore, one aspect of the present invention is the development of a pharmacokinetic/pharmacodynamic (PK/PD) model for characterizing and predicting responses to rHuEPO thereby identifying the most efficient, cost effective, and/or convenient treatment regimens for patients. In a particular embodiment of the present invention, once-weekly or once every two weeks EPO administration is contemplated. Another aspect of the present invention provides a methodology to evaluate the pharmacokinetic and pharmacodynamic profiles of EPO after administration of two or more dosing regimens for comparison of clinical outcomes along with tolerance and safety parameters between the EPO dosing regimens. Associated business methods and computer systems are also contemplated.
A specific embodiment of the present invention may include a method for obtaining optimized EPO dosage regimens for a desired pharmacodynamic response, which can comprise choosing one or more EPO dosage regimens, then using a PK/PD model to determine the pharmacodynamic profile of one or more EPO dosage regimens, and finally selecting one of the EPO dosage regimens for administration to achieve the desired pharmacodynamic (PD) response based on the EPO profile. In an additional embodiment, the PD response can comprise one or more of the group consisting of reticulocyte number, RBC number, and hemoglobin level.
An alternate embodiment of the present invention may also be a method for obtaining optimized EPO dosage regiments for a desired pharmacodynamic response which comprises first selecting one or more desired pharmacodynamic responses, then using a PK/PD model to determine a EPO dosage regimen that provides the desired responses, and finally, selecting one of the EPO dosage regimens for administration to achieve the desired pharmacodynamic response. In an additional embodiment, the PD response can comprise one or more of the group consisting of reticulocyte number, RBC number, and hemoglobin level.
An additional preferred embodiment of the present invention can include a computer program, which can be used for obtaining optimized dosage regimens for a desired pharmacodynamic response. The computer program may comprise a computer code. In a further embodiment, the computer code describes a PK/PD model for EPO and allows the user to select one or more desired pharmacodynamic responses. The computer code then uses the PK/PD model to determine EPO dosage regimens that would provide the desired pharmacodynamic responses. The EPO dosage regimen may be administered as a weekly or once every two weeks, based upon body mass, dose. Preferably, the weekly EPO dose may comprise administering EPO at a dosing of 40,000 IU and the once every two weeks EPO dosing regimen may comprise administration of EPO at a dosing of about 80,000 to about 120,000 IU. In an additional embodiment, the PD response can comprise one or more of the group consisting of reticulocyte number, RBC number, and hemoglobin level.
An alternate preferred embodiment of the present invention may include a computer program for obtaining optimized dosage regimens for a desired pharmacodynamic response. In an additional embodiment, the computer program comprises a computer code. The computer code may allow the user to select one or more EPO dosage regimens. The computer code then uses the PK/PD model to determine a pharmacodynamic response based on the EPO dosage regimens selected.
A preferred embodiment of the present invention may include computer program for determining optimized EPO dosage regimens for a desired pharmacokinetic response comprising the steps of choosing one or more EPO dosage regimens, using the PK/PD model to determine the pharmacokinetic response of the EPO dosage regimens, and then selecting the desired EPO dosage regimen based on pharmacokinetic profile, in a specific embodiment, based upon one ore more EPO or EPO-like compounds. In an additional embodiment, the pharmacokinetic response may include serum EPO levels, bioavailability, and EPO threshold levels.
A further embodiment of the present invention may include a method for obtaining optimized EPO dosage regimens for a desired pharmacokinetic response comprising the steps of first selecting one or more desired pharmacokinetic responses, then using a PK/PD model to determine a EPO dosage regimen that provides one or more of the desired pharmacokinetic responses, and finally selecting the EPO dosage regimen that provides the desired pharmacokinetic responses.
An additional embodiment of the present invention can include a computer program for obtaining optimized EPO dosage regimens for a desired pharmacokinetic response which comprises a computer code that describes a PK/PD model for EPO. In a further embodiment, the computer code may allow the user to select of one or more pharmacokinetic responses, and then use the PK/PD model to determine one or more EPO dosage regimens that provide the desired pharmacokinetic responses.
An alternate preferred embodiment of the present invention may include a computer program for obtaining optimized dosage regimens for a desired pharmacokinetic response. In an additional embodiment, the computer program comprises a computer code. The computer code may allow the user to select one or more EPO dosage regimens. The computer code then uses the PK/PD model to determine a pharmacokinetic response based on the EPO dosage regimens selected. One or more EPO or EPO-like compounds may be contemplated for use.
Another preferred embodiment of the present invention comprises a variety of methods including a business method of providing to a consumer an EPO dosing regimen that comprises a first dose of EPO followed by a second dose of EPO to a patient. The second dose of EPO is preferably administered to the patient at a time point after the first dose that coincides with the PD profile resulting from the first dose of EPO. The PD profile may include, number of progenitor cells produced in respect to time, reticulocyte concentration in respect to time, RBC number produced in respect to time, and hemoglobin concentration in respect to time. Most preferably, the PD profile will be the reticulocyte profile for this regimen. The second dose of EPO is preferably administered to coincide with the reticulocyte profile, i.e., when reticulocyte production peaks. The second dose of EPO facilitates the maturation of young red cells in the circulation into mature RBCs.
A further embodiment of the present invention comprises a business method of providing to a patient an EPO dosing regimen that comprises a first dose of EPO followed by a second dose of EPO to a patient. The second dose of EPO is administered to the patient at a time after the first dose that coincides with the reticulocyte profile of the patient. The second dose may be administered within 6 to 10 days following the first EPO dose. Preferably, the second EPO will be administered 7 days subsequent to the first EPO dose.
The business method of the present application relates to the commercial and other uses, of the methodologies of the present invention. In one aspect, the business method includes the marketing, sale, or licensing of the present methodologies in the context of providing consumers, i.e., patients, medical practitioners, medical service providers, and pharmaceutical distributors and manufacturers, with the EPO dosing regimens provided by the present invention. These include once weekly and once every two weeks EPO dosing regimens.
Another preferred embodiment of the present invention provides a method for creating a pharmacokinetic model for subcutaneous (SC) EPO administration in patients. This method can comprise obtaining pharmacokinetic data from patients, choosing an equation based the PK data collected from the patients, and fitting the PK data to the equation. In addition, obtaining the PK data may comprise normalizing serum EPO concentration values from the collected PK data and creating serum EPO concentration time profiles based on the normalized data. In a further embodiment, the PK data may be normalized by first obtaining baseline serum EPO concentration values from the PK data by averaging predose serum EPO concentration values at a plurality of time points; next, obtaining serum EPO concentration values following SC EPO administration; then, obtaining normalized serum EPO concentration values by subtracting predose EPO concentration values from serum EPO concentration values; and, finally, calculating mean normalized serum EPO concentration values at each time point.
In an additional embodiment of the present invention, the PK equation may comprise selecting the Michaelis-Menten equation. The PK data may be fitted to the PK equation using, for example, ADAPT II software and an estimate of parameters may be obtained by utilizing the least-squares by Maximum likelihood method and the extended least squares model. In a further embodiment, the parameters may be selected from the group consisting of Vmax, Km, Vd, Fr, xcfx84 (lower doses), and xcfx84 (higher doses).
A further embodiment of the present invention provides a method for calculating the bioavailability of EPO following SC EPO administration. The method may comprise obtaining PK data, calculating the area under the serum EPO concentration curve (AUC) versus dose, normalizing AUC to dose, and finally, deriving an equation by performing a linear regression of the PK data.
Another preferred embodiment of the present invention provides a method for creating a pharmacodynamic (PD) model after SC EPO administration. This method may comprise normalizing serum EPO concentrations, obtaining PD data, choosing a PD model, obtaining an equation based on the PD model, and fitting the PD data to the PD equations. In an additional embodiment, normalizing the serum EPO concentrations may comprise obtaining baseline serum EPO concentration (Cbs) for each dose group by averaging predose serum EPO concentration values at a plurality of time points for each dose group, and then, adjusting Cbs by adding Cbs to serum EPO concentration predicted by PK model and where the adjusted Cbs can be used as a forcing function for PD analysis.
In a further embodiment, the PD data may be obtained by determining the mean predose precursor cell, reticulocyte, and RBC number, and hemoglobin concentration, and then obtaining mean reticulocyte-, mean RBC-, and mean hemoglobin-versus time profiles according to EPO dose.
In an additional embodiment, the PD model may comprise a cell loss and production model. The PD data may be fitted to the model equation by using, for example, ADAPT II software, and following, both estimate and fixed parameters may be obtained by utilizing the least-squares by Maximum likelihood method and extended least squares model. Additionally, the estimated parameters can comprise Ks, SC50, and TP, while the fixed parameters may include RL, RBCL, Hb, and threshold.
A further preferred embodiment of the present invention may provide a method for predicting a PD response in a patient following various doses of SC EPO. Moreover, this method may comprise selecting a dose and dosage regimen, and then determining the PD response based on that particular dose and dosage regimen via the PK/PD model. In an additional embodiment, the PD response can comprise one or more of the group consisting of reticulocyte number, RBC number, and hemoglobin level.
The present invention can address the requirements of patients that may have deficient or inefficient EPO production relative to hemoglobin level, which may be associated with certain forms of anemia. These may include, but are not limited to, anemia associated with end-stage renal or renal failure related anemia, platinum based cancer chemotherapy related anemia, AIDS drug therapy related anemia where the drugs may include cisplatin and zidovudine. Also, patients may be undergoing autologous transfusion prior to surgery, recovering from an allogenic bone marrow transplant, suffering from rheumatoid arthritis, or an athlete or others requiring or desiring increased RBC numbers and/or hemoglobin.
The PK/PD model of the present invention has many potential therapeutic applications. For example, a physician can use this PK/PD modeling system to determine the optimal EPO dosage regimen to administer to a patient in need of increased RBC numbers and/or hemoglobin. In particular, the physician would have the option of either determining an EPO dosage regimen based on the desired pharmacodynamic outcome or determining a pharmacodynamic response based on a specific EPO dosage regimen.